A 62-year-old female was referred to our division because of general fatigue, low grade fever and exertional dyspnea for 2 months. Laboratory data and chest roentgenograms on admission revealed polycythemia vera associated with idiopathic interstitial pneumonia. Alkylating therapy with carboquone and cyclophosphamide resulted in the improvement of abnormalities on chest X-ray films which had previously shown decreased lung fields and abnormal interstitial shadows, as well as hematological abnormalities. Six months later, the results of the patient's pulmonary function tests and arterial blood gas analysis became within normal limits. Little information about polycythemia vera associated with idiopathic interstitial pneumonia is available. This case indicated that alkylating therapy with no steroidal combination is effective for idiopathic interstitial pneumonia.